Double-Oxalate-Bridging Tetralanthanide Containing Divacant Lindqvist Isopolytungstates with an Energy Transfer Mechanism and Luminous Color Adjustablility Through Eu³⁺/Tb³⁺ Codoping

Abstract

A double-oxalate-bridging tetra-Gd 3+ containing divacant Lindqvist dimeric isopolytungtate Na 10 [Gd 2 (C 2 O 4 )(H 2 O) 4 (OH)W 4 O 16 ] 2 •30H 2 O (Gd 4 W 8 ) was obtained based on the reaction of Na 2 WO 4 •2H 2 O, H 2 C 2 O 4 , and GdCl 3 in aqueous solution. Its dimeric polyoxoanion is established by two divacant Lindqvist [W 4 O 16 ] 8− segments c o n n e c t e d b y a r e c t a n g u l a r t e t r a -n u c l e a r i t y [Gd 4 (C 2 O 4 ) 2 (H 2 O) 8 (OH) 2 ] 6+ cluster. Notably, neighboring trinuclear10− polyoxoanions together, giving rise to an intriguing 3-D extended porous framework. The red emitter Eu 3+ ions and green emitter Tb 3+ ions are first codoped into Gd 4 W 8 to substitute Gd 3+ ions for the exploration of the energy transfer (ET) mechanism between Eu 3+ and Tb 3+ ions and the color-tunable PL property in the isopolytungtate system. The PL emission spectra and decay lifetime measurements of the Eu 3+ /Tb 3+ codoped Gd 4 W 8 system illustrate that under excitation at 370 nm, Tb 3+ ions can transfer energy to Eu 3+ ions. When the molar concentration of Tb 3+ ions is fixed at 0.9 and that of the Eu 3+ ions gradually increases from 0.01 to 0.08, the calculated ET efficiency (η ET ) from Tb 3+ to Eu 3+ ions increases from 7.9% for Gd 0.36 Tb 3.6 Eu 0.04 W 8 to 67.3% for Gd 0.08 Tb 3.6 Eu 0.32 W 8 . The energy transfer mechanism (Tb 3+ → Eu 3+ ) is a nonradiative dipole−dipole interaction. Furthermore, upon excitation at 370 nm, Eu 4 W 8 and Tb 4 W 8 show visible red-and green-emitting lights, respectively. When codoping trace amounts of Eu 3+ ions in Tb 4 W 8 , under excitation at 370 nm, Tb 3.92 Eu 0.08 W 8 displays near white-light emission.

Preparations, Structures and Luminescence Properties of Penta‐rare‐earth Incorporated Tetravacant Dawson Selenotungstates and Their Ho3+/Tm3+ Co‐doped Derivatives

“…The intramolecular ET in the RE co‐doped POMs can be testified by the following phenomena: (a) The emission band of the donor overlapps with the excitation band of the acceptor, so that the energy can be transferred directly from the donor to the acceptor. (b) With the increasing content of the donor, the fluorescence emission intensity of the acceptor gradually increasing . Herein, under excitation at 352 nm, Tm 3+ emission bands of Ho 3+ /Tm 3+ co‐doped materials are located at 448 and 464 nm, which overlap with the Ho 3+ broad excitation bands centered at 418, 454 and 486 nm taken by monitoring the 664 nm emission, indicating that the Tm 3+ ions can contribute to enhancing the emission intensity of Ho 3+ ions in the Ho 3+ /Tm 3+ co‐doped materials (Figure a).…”

“…(b) With the increasing content of the donor, the fluorescence emission intensity of the acceptor gradually increasing. [20] Herein, under excitation at 352 nm, Tm 3 + emission bands of Ho 3 + /Tm 3 + co-doped materials are located at 448 and 464 nm, which overlap with the Ho 3 + broad excitation bands centered at 418, 454 and 486 nm taken by monitoring the 664 nm emission, indicating that the Tm 3 + ions can contribute to enhancing the emission intensity of Ho 3 + ions in the Ho 3 + /Tm 3 + co-doped materials (Figure 4a). When Tm 3 + ions were excited by an ultraviolet light at 352 nm, electrons located at the 3 H 6 ground state of Tm 3 + cations are pumped into the 1 D 2 excited state and then part of excited electrons undergo non-radiative relaxation return to the 1 G 4 state because of the spin-orbital coupling interaction, the remaining electrons degenerate to the 3 F 4 state leading to the emission band of 448 nm.…”

“…3 T 1u non-radiative transition because of spin-orbit coupling interaction. [20] Furthermore, when electrons return from the 3 T 1u triplet state to the 1 A 1g ground state, some of them are trapped by Ho 3 + ion, enhancing the emission transitions of 5 F 4 + 5 S 2 ! 5 I 8 (575 nm) and 5 F 5 !…”

Controlled Synthesis and Properties of 3d–4f Metals Co-doped Polyoxometalates-Based Materials

“…As depicted in Fig. 15 a, upon excitation at 396 nm, the emission spectrum of EuCrMo 6 displays five prominent f − f emitting peaks at 674, 685, 690, 707, and 734 nm that are assigned to Eu 3+ 5 D 0 → 7 F J ( J = 0, 1, 2, 3, 4) transitions [ 35 ]. It is worth to note that the strong PL peak of Eu 3+ is at 707 nm in EuCrMo 6 microflakes.…”

“…According to the previous reports, the PL lifetime of Eu 3+ is about 3 ms and ca. 200 µs in nanoparticles and traditional single-crystal compounds, respectively [ 35 , 36 ]. In this work, the PL lifetime of Eu 3+ is reduced to 1.14 µs, some reasons contribute to the changing of PL lifetime.…”